Trastuzumab deruxtecan (T-DXd; DS-8201) in patients (pts) with HER2-expressing unresectable or recurrent biliary tract cancer (BTC): An investigator-initiated multicenter phase 2 study (HERB trial).
Authors: Akihiro Ohba, Chigusa Morizane, Yasuyuki Kawamoto, Yoshito Komatsu, Makoto Ueno, Satoshi Kobayashi, Masafumi Ikeda, Mitsuhito Sasaki, Junji Furuse, Naohiro Okano, Nobuyoshi Hiraoka, Hiroshi Yoshida, Aya Kuchiba, Ryo Sadachi, Kenichi Nakamura, Naoko Matsui, Yoshiaki Nakamura, Wataru Okamoto, Takayuki Yoshino, Takuji Okusaka
Journal: Journal of Clinical Oncology (2022)

4006 Background: BTCs have an aggressive tumor biology with limited treatment options. With a HER2-positivity rate of 5–20% in BTCs, case series and small clinical trials have shown signs of activity for HER2 blockade in these pts. T-DXd is an antibody-drug conjugate composed of a humanized monoclonal anti-HER2 antibody, a cleavable linker, and a topoisomerase I inhibitor. The HERB trial is an investigator-initiated, multicenter, single-arm phase 2 trial of T-DXd in pts with HER2-expressing BTCs. Methods: Centrally confirmed HER2-expressing (HER2-positive: IHC3+ or IHC2+/ISH+, and HER2-low-expressing [HER2-low]: IHC/ISH status of 0/+, 1+/-, 1+/+, or 2+/-) pts with BTCs who were refractory or intolerant to gemcitabine containing regimen received 5.4 mg/kg of T-DXd every 3 weeks. The primary endpoint was the confirmed objective response rate (ORR) in HER2-positive pts by independent central review. The sample size of 22 had 80% power with one-sided alpha error of 5%; threshold ORR, 15%; and expected ORR, 40%. The ORR, disease control rate (DCR), progression-free survival (PFS), overall survival (OS) in HER2-positive/-low pts, and incidence of treatment-emergent adverse events (TEAEs) were assessed as secondary endpoints. Results: A total of 32 pts, 24 with HER2-positive and 8 with HER2-low BTCs, received T-DXd. Twenty-two pts with HER2-positive, excluding 2 ineligible pts, were identified for primary efficacy analysis. Among the 22 pts, IHC3+ and IHC2+/ISH+ were 45.5% and 54.5%, primary sites: gallbladder/extrahepatic/intrahepatic/Vater were 11/6/3/2, median number of prior regimens was 2 (range, 1–4). The confirmed ORR in HER2-positive pts was 36.4% (8/22; 2 CR and 6 PR; 90% CI, 19.6–56.1), indicating statistically significant improvement in ORR (P = 0.01). The DCR, median (m) PFS, mOS were 81.8% (95% CI, 59.7–94.8), 4.4 months (mo) (95% CI, 2.8–8.3), 7.1 mo (95% CI, 4.7–14.6), respectively. In addition, encouraging efficacy were seen even in HER2-low pts; ORR, DCR, mPFS, and mOS were 12.5% (1/8; 1 PR; 95% CI, 0.3–52.7), 75.0% (95% CI, 34.9–96.8), 4.2 mo (95% CI, 1.3–6.2), and 8.9 mo (95% CI, 3.0–12.8), respectively. In the safety analysis set (n = 32), TEAEs of &gt; = grade (G) 3 occurred in 81.3% (26/32); the common TEAEs were anemia (53.1%), neutropenia (31.3%), and leukopenia (31.3%). TEAEs leading to drug discontinuation occurred in 8 pts (25.0%). Eight pts (25.0%) had interstitial lung disease (ILD; G1/G2/G3/G5 were 3/1/2/2) not adjudicated by an independent committee. Conclusions: T-DXd showed promising activity in pts with HER2-expressing BTCs. Although the safety profile was generally consistent with other T-DXd studies, ILD, an important identified risk of T-DXd, requires more careful monitoring and intervention. These results support further exploration of T-DXd in this patient population. Clinical trial information: JMA-IIA00423.